It is known that an aircraft, in particular a transport airplane, is generally equipped with various systems intended to monitor the environment of the aircraft (air traffic, terrain overflown, etc.) so as to be able to detect events liable to be dangerous for this aircraft, such as a risk of collision with another aircraft or with the terrain overflown for example. When such a system emits an alert, the pilot of the aircraft generally monitors his navigation screen, for example of ND (“Navigation Display”) type, to get an appreciation of the real situation of his aircraft with respect to its environment, in particular in the case of an alert relating to a risk of collision with another aircraft. Now, it may happen that the display configuration existing at this instant on the navigation screen cannot provide the pilot with the sought-after information. Also, to get good sight of the real state of the environment, it is frequently the case that the pilot must, in an often stressing alert situation such as this, modify the display mode and/or the scale of the navigation screen to obtain the appropriate image for managing the current situation. Such manual adjustment may cause him to lose time, in particular in the case where several manipulations on each of the two associated control buttons are necessary. Such a solution is therefore not satisfactory.